How to make a waterproof clock?

I really hope someone can help me. I really need a clock I can have outside. I teach classes outside and I need to know what time it is. Waterproof clock prices are exorbitant... I bet they're easy to make. Nothing comes up when I google waterproof clock works. I have this huge metal disk I found by the side of the road and it would be cool to make that into a gigantic outdoor clock. But how to make sure it's not destroyed the first time it rains...?
Can anyone help? THANK YOU!

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I have one of those bird clocks that has a different bird song for each hour. I loved having it on my covered back porch for over a year but now every time I leave it out overnight it quits running. I bring it in for a day, reset it and it starts again but when I put it back out I have to go through the same thing again. I'm assuming it's the humidity that is causing it to stop running. Any suggestions on how to keep it chirping? I've tried covering the back with duck tape but that didn't work.

True; they're not cheap and some customer reviews I've read are disappointing. If you have a house or garage window close to the area where you teach, lean a large clock in the windowsill facing outward. As for making one to leave outside, get a small 'dollar store' battery clock and slip it into a cleaned out peanut butter jar...or into an empty bird feeder hanging from a branch or on a pole? Hope this helps....

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